1. Field of the Invention
The present invention is generally related to the field of semiconductor processing, and, more particularly, to a method of forming a layer of photoresist above a process layer formed above a semiconducting substrate.
2. Description of the Related Art
In general, semiconductor devices are manufactured by forming many process layers comprised of various materials above a semiconducting substrate, and, thereafter, removing selected portions of the layers, i.e., patterning the layers. This patterning may be accomplished using known photolithography and etching processes to define the various features of the device, e.g., the gate insulation layer, the gate electrode, sidewall spacers, metal lines and contacts, etc. This forming and patterning of the process layers is typically performed layer by layer as the individual layers are formed, although multiple layers may be patterned at any given time.
Photolithography is a common process used in patterning these various layers. Photolithography typically involves the use of a product known as photoresist. In general terms, photoresist is a product that may be changed from a relatively soluble state to a relatively insoluble state by exposure to a light source. There are positive and negative photoresist currently available on the market.
In general, the photolithography process involves forming a layer of photoresist above a previously formed process layer, and exposing selected portions of the layer of photoresist to a light source to form a pattern in the photoresist that is desired to be formed in the underlying process layer. All of these steps are typically performed in well-known photolithography modules that include a section for depositing the photoresist on the wafer, e.g., a spin-coating station, a device for selectively exposing portions of the photoresist layer to a light source through a reticle, e.g., a stepper, and a section for rinsing and developing the photoresist layer after it has been selectively exposed to the light source. Thereafter, an etching process, such as a plasma etching process, is performed to remove portions of the underlying process layer that are not covered by the patterned layer of photoresist, i.e., the patterned layer of photoresist acts as a mask. After the etching process is complete, the patterned photoresist layer is removed so that additional process layers may be formed above the now patterned process layer.
The purpose of the photoresist application step is to form a thin, uniform, defect-free film of photoresist above the substrate surface. A typical layer of photoresist may have a thickness varying from approximately 1500-15,000 xc3x85, and it usually is required to have a uniformity of xc2x1100 xc3x85. Typically, when resist types are switched, and/or the target thickness of the layer of photoresist is changed, test wafers are run to determine the thickness of the photoresist produced by the system. In particular, when photoresist types are switched and/or when the supply of photoresist material is replenished, variations in the viscosity of the photoresist may also adversely impact the formation of layers of photoresist. For example, since the viscosity of the photoresist material is a factor in determining the thickness of a layer of photoresist, test wafers may also be run to determine the thickness of the photoresist layers produced using the new or replenished material. All of these qualification processes are time consuming and generally contribute to less efficient semiconductor manufacturing operations.
The present invention is directed to a method of solving or at least reducing some or all of the aforementioned problems.
The present invention is directed to a method and system for controlling the thickness of a layer of photoresist based upon the viscosity of the photoresist. In one illustrative embodiment, the method comprises sensing a viscosity of the photoresist material to be applied above a process layer, and providing the sensed viscosity to a controller that determines, based upon the sensed viscosity, at least one parameter of a photoresist application process that will be used to apply the photoresist above the process layer. The method concludes with applying the photoresist material using the application process that includes the determined parameter.
With respect to the novel system disclosed herein, in one illustrative embodiment, it is comprised of at least one sensor for sensing the viscosity of the photoresist material, and a controller that receives the sensed viscosity and determines, based upon the sensed viscosity, at least one parameter of the application process used to apply the photoresist material above a process layer. The system further comprises a tool for applying the photoresist material using an application process that includes the determined parameter.